Laminated safety glass is widely used in motor vehicle windscreens, as bullet-proof glass, for example for protecting bank and post office counters, and as window glass, for example for reducing the danger of injury in the event of breakage and also, for example, as a safeguard against burglary and theft.
The interlayers used in these laminated glasses have to satisfy numerous, very stringent requirements. The following properties, in particular, are of considerable importance, especially for the use of laminated glass in motor vehicles:
1. A high energy-absorbing capacity in the event of sudden stressing as encountered on impact with blunt, but also sharp-edged bodies.
2. Adequate glass adhesion which is intended to prevent the glass from shattering to any significant extent and causing injuries in the form of cuts in the event of accidents.
3. High translucency; no hazing or clouding should occur.
4. A high degree of light stability, in other words the windscreens should not turn yellow, even after prolonged exposure to sunlight.
5. High edge stability so that, when stored before fitting, the windscreens should not undergo any delamination from the edges through the absorption of water.
These properties in general and those mentioned under (1) and (2) in particular should be retained over as wide as possible a temperature range in which these materials are used.
In modified form, these requirements also apply to the use of the interlayers in armoured glass and in safety glass of the type used in building construction. Armoured glass is above all required to be bullet proof to a large extent. This makes it necessary to use an extremely tough interlayer.
Polyurethane interlayers for laminated safety glass are already known. Thus, according to German Offenlegungschrift No. 2,302,400 (corresponding to U.S. Pat. Nos. 3823060 and 3900446), polyurethane interlayers for laminated safety glass are produced from 4,4'-methylene-bis-(cyclohexylisocyanate), a polyester containing terminal hydroxyl groups and having a melting point above 42.degree. C. and a molecular weight of from 500 to 4,000, being the condensation product of a dicarboxylic acid and a diol compound, and a chain extender which is an aliphatic or alicyclic diol containing from 2 to 16 carbon atoms.
Unfortunately, conventional polyurethanes have the serious disadvantage of poor adhesion to glass. However, glass-plastics laminates are intended to be of a structure such that no splinters of glass can be released from the plastics interlayer of the laminated glass in the event of a collision. This requirement is not satisfied by conventional polyurethanes (cf. Example 7).
Accordingly, the object of the present invention is to obviate the above-mentioned serious disadvantage of conventional polyurethanes and, in addition, to provide polyurethane polyaddition products of the type which, in addition to excellent adhesion to glass, show outstanding impact strength over a wide temperature range, are free from hazing and local swellings, do not discolor on exposure to sunlight and show excellent edge stability with respect to penetrating water.
This object is achieved by the polyurethane polyureas provided by the invention.